General Synthesis of Mixed Semiconducting Metal Oxide Hollow Spheres with Tunable Compositions for Low-Temperature Chemiresistive Sensing

Mussel-inspired interface deposition strategy for mesoporous metal-phenolic nanospheres with superior antioxidative, photothermal and antibacterial performance

Metal-phenolic networks (MPNs) have emerged as a versatile and multifunctional platform applied in bioimaging, disease treatment, electrocatalysis, and water purification. The synthesis of MPNs with mesoporous frameworks and ultra-small diameters (<200 nm), crucial for post-modification, cargo loading, and mass transport, remains a formidable challenge. Inspired by mussel chemistry, mesoporous metal-phenolic nanospheres (MMPNs) are facilely prepared by direct deposition of the metal-polyphenol complex on the interface of oil nano-droplets composed of block copolymers/1,3,5-trimethylbenzene followed by a spontaneous template-removal process. Due to the penetrable and stable networks, the oil nano-droplets gradually leak from the networks driven by shear stress during the stirring process. As a result, MMPNs are obtained without additional template removal procedures such as solvent extraction or high-temperature calcination. The materials have a large pore size (∼12.1 nm), uniform spherical morphology with a small particle size (∼99 nm), and a large specific surface area (49.8 m2 g-1). Due to the abundant phenolic hydroxyl groups, the MMPNs show excellent antioxidative property. The MMPNs also have excellent photothermal property, whose photothermal conversion efficiency was 40.9 %. Moreover, the phenolic hydroxyl groups can reduce Ag+ in situ to prepare Ag nanoparticles loaded MMPNs composites, which have excellent inhibition performance of drug-resistant bacteria biofilm.

Confinement Enrichment Effect in HoMS-BaTiO3 Microwave Gas Sensors for the Detection of 10 ppb-0.55 v/v% Ammonia at Room Temperature

The construction of ammonia gas sensors with wide detection ranges is important for exhalation diagnosis and environmental pollution monitoring. To achieve a wide detection range, sensitive materials must possess excellent spatial confinement and large active surfaces to enhance gas adsorption. In this study, an ammonia microwave gas sensor with a wide detection range of 10 ppb-0.55 v/v% at room temperature was fabricated by incorporating hollow multishelled-structured BaTiO3 (HoMS-BaTiO3). The effect of the number of shells and the quantity of the sensitive material on the gas-sensing performance was investigated, and two-layered HoMS-BaTiO3 demonstrated the best response at high concentrations (0.15-0.55 v/v%). Conversely, single-layered HoMS-BaTiO3 displayed outstanding performance at low concentrations (10 ppb-0.15 v/v%). The lower the quantity of the sensitive material, the higher the response. This study offers a method for preparing room-temperature ammonia sensors with a wide detection range and reveals the link between the structure and quantity of sensitive materials and gas-sensing performance.

Monodispersed CuO nanoparticles supported on mineral substrates for groundwater remediation via a nonradical pathway

Nonradical oxidation based on singlet oxygen (¹O₂) has attracted great interest in groundwater remediation due to the selective oxidation property and good resistance to background constituents. Herein, recoverable CuO nanoparticles (NPs) supported on mineral substrates (SiO₂) were prepared by calcination of surface-coated metal-plant phenolic networks and explored for peroxymonosulfate (PMS) activation to generate ¹O₂ for degrading organic pollutants in groundwater. CuO NPs with a close particle size (40 nm) were spatially monodispersed on SiO₂ substrates, allowing highly exposure of active sites and consequently leading to outstanding catalytic performance. Efficient removal of various organic pollutants was obtained by the supported CuO NPs/PMS system under wide operation conditions, e.g., working pH, background anions and natural organic matters. Chemical scavenging experiments, electron paramagnetic resonance tests, furfuryl alcohol decay and solvent dependency experiments confirmed the formation of ¹O₂ and its dominant role in pollutants removal. In situ characterization with ATR-FTIR and Raman spectroscopy and computational calculation revealed that a redox cycle of surface Cu(II)-Cu(III)-Cu(II) was responsible for the generation of ¹O₂. The feasibility of the supported CuO NPs/PMS for actual groundwater remediation was evaluated via a flow-through test in a fixed-bed column, which manifested long-term durability, high mineralization ratio and low metal ion leaching.

Controllable synthesis of iron-polyphenol colloidal nanoparticles with composition-dependent photothermal performance

Iron-polyphenol nanoparticles are usually prepared with nontoxic plant polyphenols as a main building block, which are an emerging photothermal agent for photothermal therapy. However, till now, few works have been made on the controllable synthesis of iron-polyphenol nanoparticles with tunable composition, as well as investigation of the relationship between material composition and photothermal property. In the present study, iron-polyphenol colloidal nanoparticles with tunable diameter (21-303 nm) and ion content (9.2-97.6 mg/g), as well as high colloidal stability are successfully synthesized using different polyphenols (such as tannic acid, epigallocatechin gallate, gallic acid, epicatechin and proanthocyanidin) as a ligand. In addition, photothermal performance is highly dependent on the organic ligand, iron content and particle size. Higher iron content and smaller diameter can contribute to higher photothermal performance. The iron-polyphenol nanoparticles with the optimal iron content and particle size are selected as a photothermal agent. They can effectively inhibit the tumour growth in vivo. The current work demonstrates a general synthesis strategy for iron-polyphenol colloidal nanoparticles with tailorable composition and clarifies the relationship between material composition and photothermal performance. Moreover, it is conductive to the rational design of polyphenol-based photothermal agents for theranostic applications.

Yolk-shell (Cu,Zn)Fe2O4 ferrite nano-microspheres with highly selective triethylamine gas-sensing properties

Multicomponent spinel ferrites are essential to be used in high-performance gas-sensing materials. Herein, multinary (Cu,Zn)Fe2O4 spinel nano-microspheres with tunable internal structures, including solid, core-shell, and yolk-shell, were successfully synthesized by a simple self-templated solvothermal method combined with a subsequent annealing strategy. The internal structures of the (Cu,Zn)Fe2O4 nano-microspheres significantly rely on the heating rates of the precursors, which show promising selective response towards trimethylamine gas. Among them, the as-formed yolk-shell (Cu,Zn)Fe2O4 nano-microspheres exhibited high response to triethylamine with excellent selectivity of STEA/SX = 1.86 at 160 °C, fast response-recovery rate (58 s/136 s), and long-term repeatability and stability of more than one month. The corresponding triethylamine gas-sensing mechanism with the special microstructures is discussed. This work provides new insights into the rational design of interior structure and the modulation of high gas response and selectivity of multinary spinel ferrites in gas-sensing applications.

Microwave-Assisted Synthesis of Hollow Microspheres with Multicomponent Nanocores for Heavy-Metal Removal and Magnetic Sensing

The primary advantage of a hollow structure is the likelihood of introducing diverse components in a single particle to achieve multiple missions. Herein, hollow microspheres with multicomponent nanocores (HMMNs) have been prepared based on a template-free strategy via a microwave-assisted hydrothermal treatment of Chlorella. The resulting HMMNs retain the near-spherical hollow morphology and functional groups of the cell wall of Chlorella, obviating the need for templates and chemical modification. The elements (iron, cobalt, calcium, magnesium, chlorine, and phosphorus) naturally present within the Chlorella cells react to form hydroxyapatite/chlorapatite and magnetic nanocores without the need for exogenous chemical reagents. The performances of HMMNs for cadmium ion (Cd²⁺) removal and antibiotic detection are explored. HMMNs exhibit relatively high adsorbance of Cd²⁺ (1035.8 mmol/kg) and can be easily recovered by application of an external magnetic field. Ion exchange with Ca²⁺ and Mg²⁺ is shown to be the main mechanism of Cd²⁺ elimination. In addition, HMMNs are a suitable carrier for the construction of a magnetic immunosensor, as demonstrated by the successful development of such an immunosensor with acceptable analytical performance for the detection of neomycin in milk samples. The versatile applications of HMMNs result from their multicomponent nanocores, hollow structure, and the functional groups on their shell. This work not only offers a simple and eco-friendly strategy for the fabrication of novel HMMNs but also provides a valuable advanced material for contaminant detection and heavy-metal removal.

Synthesis of gadolinium/iron-bimetal-phenolic coordination polymer nanoparticles for theranostic applications

Integration of diagnostic and therapeutic components into a single coordination polymer nanoparticle is desirable for theranostic applications, but still challenging. Herein, we report the synthesis of bimetal-phenolic coordination polymer nanoparticles using gadolinium nitrate and ferrous sulphate as a metal source, and plant polyphenols (i.e., tannic acid) as an organic ligand via a metal-catechol coordination assembly process. Such coordination polymers show a tunable molar ratio of Gd/Fe and high dispersibility and stability in aqueous solution. The coordination polymers reveal composition-dependent performance for longitudinal relaxivity and photothermal conversion. The longitudinal relaxivity is positively related to the molar ratio of Gd/Fe, while the photothermal performance is negatively related to the molar ratio of Gd/Fe in the coordination polymers. The coordination polymers with an optimized molar ratio of Gd/Fe exhibit an ultra-small hydrodynamic diameter (∼23 nm), a high r₁ value (9.3 mM^-1 s^-1) with low r₂/r₁ (1.26) and high photothermal conversion efficiency (η = 37%). They can be used as a contrast agent for T₁-weighted magnetic resonance imaging of EMT-6 tumor bearing mice, which can effectively enhance the signals of tumors. They can also effectively suppress tumor growth via photothermal therapy. This work brings new insights for the synthesis of multifunctional coordination polymer nanoparticles and extending their potential applications in theranostics.